1. Field of the Invention
The present invention relates to bases for heat sinks, and particularly to bases consisting of two different metals for improving heat conductivity.
2. Prior Art
Computer electronic devices such as central processing units (CPUs) frequently generate large amounts of heat, which can destabilize operation and cause damage. A heat sink placed in thermal contact with an electronic device mounted on a socket transfers heat from the electronic device through conduction.
A conventional heat sink comprises a base and a plurality of fins extending upwardly from the base. A central portion of the base is secured in contact with an electronic device, to conduct heat from the device to a top surface of the base. The heat is then conducted to the fins and dissipated by the fins. The base is often integrally made of aluminum or aluminum alloy. Aluminum and aluminum alloy have relatively low coefficients of heat conduction. Thus the heat generated by the device is not effectively transferred to the top surface of the base.
Improvements on such bases have been developed. FIGS. 4 and 5 show an improved base 2. The base 2 comprises a body 3 made of aluminum, and a plate 4 made of copper. The body 3 defines a recess 5 in a bottom surface thereof. The plate 4 is fixed within the recess 5 by means of welding with an intermediate layer of tin 6. The plate 4 contacts an electronic device to transfer heat from the device to the body 3. Unfortunately, the coefficient of heat conduction of tin (67 w/cm. k) is much lower than that of copper (359 w/cm. k) and that of aluminum (207 w/cm. k). Thus the layer of tin 6 between the plate 4 and the body 3 retards heat conduction between the plate 4 and the body 3, thereby reducing the efficiency of heat dissipation.